Pulse-code modulation (PCM) systems typically utilize transmission of digitized signals of quantized and coded information. Quantization is generally achieved by selecting a number of discrete pulse amplitude levels. Quantization may be linear, by utilizing uniformly spaced levels, or nonlinear, by utilizing nonuniformly spaced levels. Digitization provides for one-to-one correspondence between each level and a set of real integers, typically digits expressed in a coded, often binary, form. For example, a system quantized to eight levels could be binary coded 000, 001, 010, 011, 100, 101, 110, and 111, each binary code representing a pulse code data stream of 1's and 0's for a next higher level. Each pulsed waveform is thus effectively reduced to a set of digits at successive sample times. Instead of transmitting individual samples at selected sample times, a pulse code is sent at the selected sample times, thereby providing information in quantized form.
In simulcast PCM communication systems differential delays and Doppler shifts often cause distortion of received signals, thereby also making determination of termination of multi-level digital signal data streams difficult. Data stream termination detectors that rely on a single sampling interval have been described in the prior art. Such detectors, however, where sampling is started too late into a sample interval to permit a correlator from amassing enough correlation occurrences, may discard vital termination information, thereby failing to provide accurate termination information. There is a need for an improved device and method for determining the termination of multi-level digital signal data streams.